1. Field of the Invention
The present invention relates generally to electrical-power demand registers and methods. More particularly, the present invention is directed to a solid-state electrical-power demand register and method employing a nonvolatile read/write memory which retains stored data even when deenergized, and also employing error detection and correction of data.
2. Description of the Related Art
Customer electrical loads draw electrical power from an electrical utility. For the utility to be capable of supplying electrical power to all its customers under worst-case conditions, the utility must be able to predict the peak power demand of each customer and have sufficient power-generating capacity to meet the worst-case peak demand. Failure to be able to meet the worst-case peak demand results in brownouts or even blackouts, which subject the utility and its customers to adverse consequences.
The larger the worst-case peak demand, the greater the peak power-generating capacity of the utility must be. If customers can reduce peak demands, the utility can concomitantly reduce reserve power-generating capacity. The reduced reserve capacity will ultimately be reflected in lower bills to the customers.
To foster customer reduction of peak demands, two types of metering arrangements or registers have developed to provide the customer and the utility with needed electrical power consumption information: the demand meter or register and the time-of-day energy consumption meter or register. Briefly, a demand register indicates the peak power demand by a customer within a preselected time measurement interval, irrespective of when the demand occurs. A time-of-day, energy-consumption register, on the other hand, measures electrical-power consumption during preselected periods which are characterized according to time of day, type of day (for example, weekday, weekend, or holiday), and season (for example, summer or winter).
Turning to the demand register, there are at least three types of measurement data that can be provided: noncumulative; cumulative; and, continuous-cumulative. A noncumulative or block-interval demand register measures, stores and displays the largest electrical-power demand incurred during a measurement interval within a billing period. At the end of each billing period, the stored value is reset to zero by the meter reader or billing apparatus.
A cumulative demand register measures and stores the largest electrical-power demand incurred during a current billing period (that is, the same value measured by a noncumulative demand register). It also measures, stores and displays the running sum of the largest demands incurred during each previous billing period. At the end of the billing period, the stored value corresponding to the largest electrical-power demand for the billing period just ended is added to the running sum and is then reset to zero.
During a current billing period, continuous-cumulative demand register measures and stores as a first stored value each successive electrical-power demand which is larger than a previously largest demand that was incurred since the beginning of this billing period. Each time a higher peak is detected, the first stored value is updated with the even larger demand value, and a second stored value is increased accordingly. This second stored value corresponds to a running sum of the largest electrical-power demands incurred during previous billing periods and the largest electrical-power demand incurred up to the present time of the current billing period. Only this second stored value is normally displayed. At the end of each billing period, the first stored value is reset to zero.
Until recently, demand registers have been mechanical. Such apparatus have a register coupled to and driven by eddy-current induction motors of the type found in conventional electrical-energy usage (kilowatt-hour) meters commonly employed by utilities for billing purposes. In fact, it is not uncommon for a mechanical electrical-energy usage register (either of the time-of-day type or otherwise) also to include a mechanical demand register.
Mechanical demand registers exhibit several disadvantages. The mechanical demand register places an increased mechanical load on the eddy-current induction motor. In addition, because demand is typically measured over a fixed time interval (typically from ten to thirty minutes) means must be included to actuate the mechanical demand register for the demand-monitoring interval. This means complicates the design of the overall meter.
With the advent of solid-state electronics, electronic demand registers have been developed. These circuits are often small enough to fit inside the housing of a standard kilowatt-hour meter. Such solid-state demand registers calculate peak power demand on the basis of signals which define a demand-monitoring interval and which describe the consumption of electrical energy during the demand-monitoring intervals. Microprocessors have been employed in some solid-state demand registers.
State-of-the-art time-of-day registers also employ microprocessors. Unlike demand registers, which do not require their timing pulses to be generated in accordance with the actual time of day, a time-of-day energy-consumption register must include a backup battery so that its clock will not be turned off when electrical power to be register is cut off due to a power outage, customer tampering or the like.
In microprocessor-based, time-of-day and demand registers of recent design, random-access memories (RAMs) have been employed. A backup battery is required to energize the random access memory during a voltage dip on or failure of the alternating-current to prevent loss of data stored in such a memory.
The use of such a backup battery results in several technical deficiencies. Including a battery in a register increases its complexity, cost and maintenance requirements. Should the battery malfunction and a power mains failure or severe voltage dip occur, the data stored in the memory will be lost. Furthermore, batteries have limited life and thus require periodic replacement. In addition, the environments in which many registers are used put extreme temperature or humidity stress or both on the batteries.
These requirements point to the necessity of including some provision for ensuring and maintaining the integrity of stored computing constants and computed results. While certain demand registers of recent design employ simple data error-detection techniques such as the use of checksums, more effective error detection is required. Furthermore, these registers have not included data error-correction techniques. The lack of error-correction capability means that such registers must be removed from use and either replaced or put back in proper working condition.